1. Field of the Invention
The present invention relates to the mechanical design and electrical circuitry for an electronic combination lock. Specifically, the invention relates to such a lock wherein the handle houses the pushbuttons and is mechanically isolated from the bolt so that rotation of the handle only will open the bolt when the proper combination of pushbuttons has been depressed.
2. Description of the Prior Art
Electronic combination locks offer the advantages over mechanical locks that there is no key to lose, that the combination is easily changed, and that there are no audible clicks associated with their operation to provide information to a potential lock picker. However, certain disadvantages typify prior art electronic combination locks. These include difficulty of installation, high cost, susceptability to tampering or forced entry and high power consumption or battery drain. A principle object of the present invention is to provide an electronic combination lock which overcomes these difficulties.
Prior art mechanical and electronic locks often were difficult to install, requiring a rectangular or oblong hole to be chistled in the door or frame. Typically a housing for the lock pushbuttons had to be mounted on the outside of the door in addition to a handle that mechanically operated the bolt when the proper combination was selected. Such installation problems discouraged the average homeowner from buying such a lock. In contrast, it is another object of the present invention to provide an electronic lock that is simple to install, requiring only a drill, and in which the pushbuttons are housed within the handle itself.
The complicated mechanical assemblies and electronic circuitry associated with prior art electronic combination locks lead to high cost. A further object of the present invention is to provide an electronic combination lock wherein simplified construction using few parts, many of molded plastic, results in low cost. A combined handle and pushbutton construction eliminates parts, simplifies operation, and reduces both manufacturing and installation costs.
Prior art electronic combination locks were susceptible to tampering in several ways. In some, the direct mechanical connection between the handle and the bolt permitted forced entry. In others, the electrical circuitry did not include sufficient safeguards to prevent unauthorized lock actuation, as for example by rapidly depressing random sets of pushbuttons.
Thus a further object of the present invention is to provide an electronic combination lock in which the handle is isolated from the bolt so as to prevent forced entry, and in which the electronic circuitry has sufficient safeguards so as to prevent unauthorized operation by someone who does not know the correct combination.
High power consumption or battery drain is typical of some electronic combination locks. For example, in some locks the bolt itself is moved by a solenoid or other electromechanical device. Considerable power is required to inpart this mechanical motion. In some lock circuits, considerable power is drawn even during the quiescent state when the lock is not being operated. In contrast, yet another object of the present invention is to provide an electronic combination lock in which the bolt is operated mechanically so as to reduce power consumption, and which uses electronic circuitry that draws substantially no current in the quiescent state.